Caption: Macrophotograph of fragments of a silicon oxide insulating material. Similar to aerogels, this form of silicon oxide has a very low density and is fairly transparent. The colour seen here is a result of the lighting used by the photographer. The fine structure of these spheres and their low density make them a very good thermal insulator. It is thought that such spheres could be used as a filling for double-glazed windows. Magnification x2.5 at 6x7cm size.